Bronchopulmonary dysplasia (BPD) is a severe iatrogenic complication and a prominent feature in chronic lung disease of mechanically ventilated infants borns prematurely. The prupose of this protocol is to investigate the pathophysiologic mechanisms of BPD and the response to drug therapy. This will be achieve by analyzing the relationship between ventilatory parameters reflecting baro-oxidative injury, and the serum levels of type I and type III procollagen propeptides, as markers of fibrosis. Response of collagen markers to dexamethasone and other medications will be investigated.